The present invention relates to mechanisms for altering the actuation of valves in internal combustion engines; more particularly, to finger follower type rocker arms having means for changing between high and low or no valve lifts; and most particularly, to a two-step finger follower type rocker arm assembly, having a fixed central cam follower and a pair of pivotable lateral cam followers disposed on the finger follower body, and having locking means for latching and unlatching the lateral cam followers from the finger follower body to shift between high lift and low lift modes.
Variable valve activation (VVA) mechanisms for internal combustion engines are well known. It is known to be desirable to lower the lift, or even to provide no lift at all, of one or more valves of a multiple-cylinder engine, especially intake valves, during periods of light engine load. Such deactivation can substantially improve fuel efficiency.
Various approaches have been disclosed for changing the lift of valves in a running engine. One known approach is to provide an intermediary cam follower arrangement which is rotatable about the engine camshaft and is capable of changing both the valve lift and timing, the cam shaft typically having both high-lift and low-lift lobes for each such valve. Such an arrangement can be complicated and costly to manufacture and difficult to install onto a camshaft during engine assembly.
Another known approach is to provide a deactivation mechanism in the hydraulic lash adjuster (HLA) upon which a cam follower rocker arm pivots. Such an arrangement is advantageous in that it can provide variable lift from a single cam lobe by making the HLA either competent or incompetent to transfer the motion of the cam eccentric to the valve stem. A shortcoming of providing deactivation at the HLA end of a rocker arm is that, because the cam lobe actuates the rocker near its longitudinal center point, the variation in lift produced at the valve-actuating end can be only about one-half of the extent of travel of the HLA deactivation mechanism.
Still another known approach is to provide a deactivation mechanism in the valve-actuating end of a rocker arm cam follower (opposite from the HLA pivot end) which locks and unlocks the valve actuator portion from the follower body. Unlike the HLA deactivation approach, this approach typically requires both high-lift and low-lift cam lobes to provide variable lift.
U.S. Pat. No. 5,655,488 issued Aug. 12, 1997, discloses a system including an inner rocker arm in engagement with a valve and with a first cam, an outer rocker arm in engagement with a second cam, and a latch member which is insertable between the rocker arms. A significant drawback of the disclosed apparatus is that the latching mechanism is a relatively large box-like member which xe2x80x9cessentially surroundsxe2x80x9d the outer rocker arms, thereby increasing undesirably the mass and inertia of the rocker assembly. Another drawback is that its outer rocker arms are inter-connected and move in unison thereby increasing the mass and inertia of the moving members.
It is a principal object of the present invention to provide a simplified variable valve lift apparatus.
It is a further object of the invention to provide an increased range of motion between a high lift and a low lift position of an engine valve.
Briefly described, a two-step finger follower rocker arm assembly in accordance with the invention is configured to cooperate with an engine camshaft having both high-lift and low-lift cam lobes. For each valve of the valve train equipped with the present rocker arm assembly, a central low-lift cam lobe is accompanied by at least one high-lift lobe and preferably is flanked symmetrically by a pair of lateral high-lift lobes.
The present rocker arm assembly includes an elongate, rigid follower body that has a socket at a first end for engaging a conventional hydraulic lash adjuster as a pivot means, and that has an arcuate pad at a second and opposite end for engaging a valve stem or lifter means. A central well or passage through the follower body contains means, preferably in the form of a fixed slider or roller, for following the central low-lift cam lobe to provide low-lift of the valve when engaged therewith. Outboard of the follower body and pivotably mounted thereupon are first and second lateral high-lift followers, including sliders or rollers, for following the lateral high-lift lobes to provide high-lift of the valve. A latch block disposed on the body is slidable by piston and spring means between first and second positions to alternatively latch and unlatch the high-lift followers. In latched position, the rocker arm assembly acts in high-lift mode; in unlatched position, in low-lift mode.